Here's a typical scenario: The hero has finally appeared at his confrontation with the Big Bad, who's seated at his big table, just about to take his evening meal. "There's no reason to be uncivil," the villain says. Would the hero like some wine? The hero takes a drink, and immediately starts choking. The villain laughs - that fool, the hero, should have known that the villain would poison the wine with the dreaded juice of the Ultramurder fruit!

But what's this? The hero's standing back up! "I knew you'd poison the wine with the dreaded juice of the Ultramurder fruit. That's why I've spent years eating small pieces of Ultramurder fruit, to develop an immunity to the poison!" The hero then kicks the villain's tail.

In some cases, the poison builds up and actually turns the poison-proof character into a Poisonous Person.

For some (chiefly organic) poisons, the body produces antibodies to clear them from the system; so, with repeated exposure to small amounts, you can build up a level of circulating antibody that grants immunity to a typical dose. In the past ages, the few metallic poisons known were rare and expensive; therefore most poisons were plant-based alkaloids. However, there are plenty of other poisons (including nearly all heavy metals to which modern civilians and industrial workers are exposed, such as compounds of lead, radium, mercury and cadmium) that don'tget cleared from the system and simply build up in your tissues until you reach a lethal dose.

Could be considered a sub-trope of Adaptive Ability. A particularly Crazy-Prepared person may be immune to several — or even all — poisons via this method, though again it's important to note that in real life, not all poisons can be defended from in this manner. This trope is often key to the survival of someone who is pulling a Self-Poisoning Gambit.

Examples:

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Anime & Manga

Killua from Hunter × Hunter is immune to virtually all forms of poison due to his family's Training from Hell, and is seen happily downing five cans of laxative-laced juice before the Hunter Exam starts.

In Ninja Scroll, Kagero's body absorbs toxins instead of processing them. It makes her ideal for working as her master's food taster, but it's also made her bodily fluids highly toxic, which is good for assassination — not so much for potential love interests. However, the kiss she and Jubei share just before she dies is implied to be enough to counteract the poison in his body.

In Apothecarius Argentum, Argent was fed a number of poisons at a young age so he could be sold as a food taster/assassin. As a side effect, they also turned his blood into some kind of killer acid, and just touching him is enough to make his love interest, the princess faint.

Assassin Shao Li from Noir kills using poisoned fingernail polish and inflicting a small nick on her victim, and in one scene she kills a man using incense that contains a poison she's built up an immunity to and remarks as he's choking on the ground that to her it just smells pleasant.

Ryuuki built up a resistance to various poisons mostly thanks to growing up as The Unfavorite at the bottom of a pecking order of six princes and their mothers. He once realized that Shuurei had been handed a poisoned drink and drank it himself before she gulped it down, counting on the trope to work; it did and he lived to tell, but it still made him rather sick.

Sa Sakujun in the same series built up a similar resistance through bored experimentation, not that it does him a lot of good in the end.

Most of the Gourmet Hunters in Toriko have resistance to various poisons due to incidental or deliberate exposure. Coco is an extreme example, having been exposed to so many toxins that he's able to synthesize them within his body, and on the rare occasion that he's hit with a poison that he ISN'T immune to, he can adjust his immune system within seconds.

Played for Laughs with Magellan, whose Devil Fruit powers allow him to manipulate and create all kinds of poisons; this naturally made him immune to poisons himself, meaning he enjoys eating poisoned meals, but doing so leaves him stuck on the toilet for ten hours a day.

Less for laughs and more for awesome after the Time Skip, when Luffy's clash with Magellan gives him immunity to a crapload of poisons. As if he hadn't taken enough levels in badass already... Though even then, his antibodies still have limits; a strong enough poison (as in, one that would cause instant death in a normal person) can still make him extremely sick.

Sanji's estranged sister Vinsmoke "Poison Pink" Reiju has this as well. At some point Luffy is very sick after being given a very powerful poison, but she went up to him and gave him a Kiss of Life to absorb it and heal him. She has no physical side-effects afterwards.

In Pokémon, Ash has gotten fried by Pikachu so many times that he's built up a near-total immunity to electric shocks, surviving jolts that were outright exploding whatever they hit in a later episode. Meowth also made use of his Pikachu-induced shockproofing once.

Once or twice Team Rocket have shrugged off electric shocks simply because they've been hit by Pikachu so many times.

AJ's Sandshrew has Acquired Water Immunity.

Zen of Snow White with the Red Hair, being a prince and thus having a good chance of being poisoned, spent an extended amount of time becoming immune to many different poisons.

Subverted in Bleach. During Mayuri's fight with Szyael, as his bankai's poisonous gases seep over to the injured Uryu and Renji, Uryu initially believes that unlike Renji, he will be safe from the poison, as he was poisoned before in his previous battle with Mayuri. Uryu then shows symptoms of poisoning, and Mayuri mocks the idea that someone could become immune to his poison, saying that it is constantly adapting itself.

In Dokuhime little girls are purchased for the purpose of bringing them up to be Poison Princesses, and exposed from the time they're in their cradles to poison in order to build up immunity. Many don't make it, the successes are trained to be assassins whose very touch is deadly. They have to keep ingesting poison to function properly.

In Akuma no Riddle, Haru Ichinose has gone through so many surgeries that she has started to become resistant to sleep-inducing drugs. Even if she does get affected, she wakes up a lot faster than a regular person would.

In a similar vein to the Pokemon example above, in Fairy Tail, the heroes face an enemy that uses colored magical confetti to produce various elemental effects. When said enemy attempts to use yellow lightning-producing confetti on Mirajane, the latter laughs, as (having had Laxus for a guildmate during his entire jerkass phase) she's been zapped enough times that the yellow confetti can't produce enough voltage to faze her.

In Brave10, this is a common part of ninja training as demonstrated by Anastasia, Saizo and Sasuke during the Goemon gang's Knockout Gas attack. They aren't immune to every kind of poison and even the ones they are cause them to become weak the longer their exposure is, but the three proper ninja of the team are all able to keep fighting even when the rest of the team is completely out because ninja are Crazy-Prepared.

In a later chapter of ''Onidere, it's revealed that Tadashi has been rendered completely immune to all forms of poison due to constantly eating his girlfriend's cooking.

On the topic of Dr Crane, apparently he's gassed himself so often he's become unable to fear anything...except Batman.

The Joker has built up immunity to his trademark poison to the point that mosquitoes writhe in pain after sucking his tainted blood.

Played for laughs in a crossover with Captain America, where the Joker and the Red Skull discover that their signature poisons are so alike that each is immune to the effects of the other.

Same deal with Harley; in her own title, she once tried to bluff Batman into thinking she was committing suicide by drinking it. (Didn't work; he knew she was immune to it.)

Also, the Joker is apparently immune to Scarecrow's fear gas, as one comic has them team up before Scarecrow sprays the Joker with his fear gas, which only resulted in the Joker smashing Scarecrow over the head with a chair.

In one instance, the fear gas caused the Joker to laugh uncontrollably.

Since it's the Joker we're talking about, it's less likely that it's a result of acquired immunity and more that he's simply too crazy to be afraid.

It's often established that Joker is immune to many toxins including his own Joker Venom due to years of dedicated substance abuse.

Wolverine has assassin Reiko invoke this trope with blowfish toxin, which Jubilee learns while dodging attacks.

Harley Quinn is immune to Poison Ivy's poisons because of all the, uh... time they spent together. In the animated series this is handwaved by having Ivy just give her a vaccine against them.

It's actually a somewhat common martial arts technique in the comics Jademan translated for US release in the 80's and 90's. Indeed, most poison immune characters could actually manipulate their immunity so they could cure someone else's poison by drawing a bit of their own blood and feeding it to them.

In one comic, Superboy deliberately exposes himself to pieces of kryptonite, to build up an immunity to those particular pieces, so he can later use them against Kryptonian criminals with being affected himself.

Nearly every depiction of one of his future incarnations has them demonstrate considerably more tolerance to the effects of Kryptonite, implying that this trope is in effect. Particularly if the story has them paired up with his counterpart from the present day, where Future!Supes will often shrug it off while the Present!Supes is vastly weakened. This depends on the incarnation, however; some continuities justify his resistance with other sources, such as a vastly increased store of solar energy.

Spider-Man seems to be developing an immunity to the gas used by the Green Goblin to nullify his Spider-Sense. Originally, the stuff rendered him unconscious and would make him unable to use the power for several days. Most recently, when the Hobgoblin used it in the "Revenge of the Sinister Six" story, he was able to stay conscious, and recover in little over one day.

Venom's symbiote has been stated to have become increasingly resilient to flames and sonics through repeated exposure. How much more resilient it's become depends on the writer.

In the comic New X-Men, Laurie Collins aka Wallflower is the daughter of Sean Garrison, a mutant with extremely powerful pheromone production and control, who had Laurie's mother Gail in his thrall until Laurie was conceived. Because Laurie inherited her father's mutation, carrying her made her mother immune to Sean's pheromones and enabled her to break free of his control.

Black Moon Chronicles: The master of the Thieves' Guild that Pilou grew up in kept the other criminals in line by putting poison in their food and providing an anti-toxin at the end of every day if they had fulfilled their quota. Pilou starts to take a small portion of the poison every day to build up an immunity so he can one day escape.

Get Fuzzy. In the strip for May 18th 2013, Bucky says that he consumed two spiders per day for the last four years to build up an immunity to poison. When Satchel points out that the spiders in their house aren't poisonous, Bucky doesn't feel so good.

The titular badger in The Urthblood Saga, among his other powers, has built up an immunity to all but the strongest poisons from this method. One poor ferret who tried to poison him and take over his army learned this the hard way...

The Princess Bride: The Man In Black challenges Vizzini to drink from two cups, one of which has been poisoned with iocaine. After they both drink and Vizzini dies, the Man in Black reveals that he poisoned both cups because he'd spent the last ten years developing an immunity to iocaine.

Under Siege 2: Dark Territory has a thug who has been pepper-sprayed so many times, all it does is clear out his sinuses. And then he proves it by using it as a breath freshener.

In Woody Allen's Bananas, Gen. Vargas has a servant on hand to taste his meals in case they are poisoned. One meal does turn out to be poisoned, but the General eats it, anyway, claiming that he's been poisoned so many times to have developed immunity.

In Thank You for Smoking, terrorists try to kill the main character by covering him in nicotine patches, which would overwhelm any normal person, and leaving him naked on the lap of the Lincoln Memorial. He survives, and recovers fairly quickly, because he'd been chain smoking for years and had built up a superhuman tolerance to nicotine. Unfortunately (fortunately?) it also means he can never smoke again.

In the 2008 movie Get Smart, 99 sprays Max with knockout gas. Max says that he developed an immunity to it, then passes out while cursing, "Oh, it's the new stuff!"

Pat Morita's character in King Cobra is a snake handler who regularly injects himself with doses of snake venom to develop immunity. He's able to shrug off getting bitten by the giant snake once, but after getting bitten a few more times, he weakens and dies.

In the third Riddick movie, Riddick has to get through a narrow pass to get out of the desert into the fertile grasslands beyond. The pass houses a muddy pool with a poisonous scorpion creature that paralyzes its prey. He captures a younger, smaller creature, and extracts the poison. He tests it on a young desert dog first, then injects himself with small doses until he's built up an immunity.

In the short film The Bloody Olive, the female lead explains to a bystander that she was vaccinated against all types of poisons, which rendered the villain's poison dart ineffective.

Literature

In Kim Newman's The Hound of the D'Urbervilles, in a international meeting of bad guys, Rupert of Hentzau passes around a flask that no one takes, since nobody trusts the others. Even after Rupert openly takes a drink, Colonel Moran thinks to himself that he could have built up an immunity, and mentions that Madame Sara (another Victorian villain) who does take a drink, likely has made herself immune to all poisons.

The murderer in the Lord Peter Wimsey novel Strong Poison builds up an immunity to arsenic in this way. This does not work in Real Life... though the reference books Lord Peter reads really do exist, and they really do claim it could work.

A novel or two mentions a food-taster who has ingested so many poisons that he's not only immune to them, but can recognize them by taste (very handy). He can also tarnish silver by breathing on it (not so handy). And reputedly eats a toad a day to stay in practice.

The vampires in Carpe Jugulum have also built up a resistance to garlic, sunlight, holy water, vampiric OCD, and holy symbols by this method. It backfires, sort of. When they lose the immunity, they realize they're surrounded by the shapes of holy symbols they wouldn't recognize if they hadn't been shown so many different ones becoming immune in the first place.

Played with in Mort. The first King that Mort sees die asks Death how he was killed. Death explained it was by a crossbow. The king laughed and said "And here I have been making myself immune to all of these poisons. There's no immunity to cold steel, eh?"

In The Count of Monte Cristo, old Monsieur Noirtier survives a murder attempt using poison because he has been taking a medicine that contains the same compound, and has built up a resistance to it. Realizing that his granddaughter and heir Valentine is also a target, he starts giving her small doses of his medicine; this saves her life when the poisoner has a go at her. The poisoner later tries again using a different poison, but by then Valentine's Love Interest Maximilien has called in his friend the Count of Monte Cristo, who saves the day in his own inimitable style.

Poisoning is the de facto assassination method of the Nyissans in the Belgariad. So much so that any government official who lives for very long (case in point: Sadi) has not only long since acquired immunity to some poisons, but is trained to recognize many more, and doses himself with antidotes frequently, just in case. It's explicitly noted that the poisons taste much better than the antidotes.

In the Dashiell HammettContinental Op short story "Fly Paper" (1929) a woman wants to poison her abusive boyfriend, but is afraid he'll be suspicious if she gives him something without drinking it herself. After reading The Count of Monte Cristo she takes small doses of arsenic (extracted from fly paper) to build up an immunity, but instead fatally poisons herself. In discussing the case afterward the detectives reveal that the book is wrong; while some people have a natural resistance to arsenic, it's not possible to build up an immunity through controlled exposure. The poison of choice in The Count of Monte Cristo is in fact Brucine, and is subject to Mithridatism.

The eponymous heroine of the Angelique novels by Anne Golon (set during King Louis XIV's reign) survives an assassination attempt when the killers force her to drink a cup of poison. Unbeknownst to them, she had already taken for some years a pill each day, filled with minute amounts from the most common poisons of that age. This got played realistically, as despite the acquired tolerance and the fact she throws up just after the assassins leave, she still got very sick for the next few days and barely survived.

The A. E. Housman poem "Terence, This Is Stupid Stuff"" retells the legend of Mithridates, a king who over the course of his life ate small doses of poison in his food to slowly build an immunity to poisons and thus foil potential assassins. This story is used as an allegory; Housman's poem claims that the purpose of his poetry is to inoculate the reader against the evils of the world by describing them in palatable verse.

Liz Williams' The Poison Master averts this: the Master Ari Ghairen modifies his own body with spider and snake genes to be both resistant and toxic, in an effort to keep up with the cold war in his Guild.

The Dornish in A Song of Ice and Fire are rumoured to put extremely low doses of snake venom in their food along with all the spices, which may be an allusion to this trope. It's supposedly done more for the mild numbing, tingly effect and/or Macho Masochism (a la fugu) than a conscious attempt to build up immunity, though... that is, if it's not just a lie they tell to outsiders.

In Kalki's classic Tamil novel Sivakamiyin Sabadam (Sivakami's Vow), the villainous monk Naga Nandi builds up an immunity to cobra venom. It gets to the point that it runs through his veins instead of blood, and cobras come flocking to him, attracted by the scent.

This is a plot point in Sharyn McCrumb's novel If I'd Killed Him When I Met Him.

Harnrim Starangh, a Red Wizard from Elminster's Daughter. "It had taken two years of retching weakness to build up a resistance to killing doses of staeradder", but being able to use a fast-acting poison freely was worth it, since his most dangerous foes were other wizards whom he couldn't expect to quickly defeat by magic.

In The Hunger GamesPresident Snow tried to build up a resistance to all of the poisons used to kill his opponents, but wasn't always successful, hence the smell of blood.

In ''The Journey of The Catechist" Etjole Ehomba can talk to animals, and a snake puts a very slight poison into his waterskin due to his politeness. He then shrugs off a poisoned dart after having built up an immunity. At which point the dart shooter decides to switch to much more effective magic, and kills Etjole outright.

The Disgaeanovels gives an explanation as to why Laharl survived being poisoned by Etna in the game, the reason was that his crazy aunt Yasurl gave him the same poison when he was little and in her care.

In Best Served Cold by Joe Abercrombie, poison-master Morveer keeps himself resistant to many of his own poisons by regularly consuming them.

In the Gaunt's Ghosts novel Traitor General it is mentioned that the Nihtgane partisans have built up immunity to the poisons in the Untill fauna.

Sam of Villains by Necessity has developed one of these to every poison he's likely to encounter in his career as an assassin — except alcohol. He actually chides his Evil Twin for poisoning a knife with a toxin they are both immune to while they fight.

Malus Darkblade develops dermal immunity to poison after years of smearing himself with venomous slime of the huge fearsome lizard he uses as a mount, which he'd been doing so that the beast would allow him near it.

In Agatha Christie's Curtain, Hercule Poirot drugs the murderer using his own sleeping pills, which he has been taking for many years. He uses the same gambit as Westley does in The Princess Bride, poisoning both cups while implying that only one cup is poisoned.

A plot point in Gary Jennings' Raptor, becoming something of a Chekhov's Gun. The idea is that a person can become poisonous, by taking small amounts of poison, and kissing or sleeping with that person will poison his or her partner.

Speaking of Jennings, in Aztec, the travelers all take their snakebite prevention medicine, which involves being injected with venom from a tooth of each kind of poisonous snake. The doctor who performs the procedure advises Mixtli that his bite will now be venomous; when he finds out it's not, he assumes he is not immune to snakebite.

In the Paradox novel Even the Wingless after almost being poisoned with hekkret, a recreational drug for the Chatcaava but a deadly poison to most Alliance races, Eldritch ambassador Lisinthir starts smoking small amounts of hekkret to build up an immunity. Unfortunately he becomes addicted, and it doesn't provide total immunity against the daily attempts to poison him as he starts vomiting blood.

Phoenix and Ashes: The aftermath of his World War I experiences has Reggie taking lots of sedatives in order to sleep at night (enough that he's getting concerned). Alison isn't aware of this, so when she injects him with opiates to keep him prisoner the dosage isn't nearly enough to do the job.

In the Tales of the Five Hundred Kingdoms book The Snow Queen, the Godmother Aleksia is using her Magic Mirror to gather information on a tyrant that she will need to deal with. She notes that the tyrant visits his Alchemist daily for a concoction made of thirty common poisons, which gives him an immunity to all but truly exotic poisons (and the reason why he doesn't need to employ a tester). For the truly exotic poisons (which are usually slow acting), the alchemist would have the antidote handy.

The Dresden Files: Harry Dresden does a mental version of this in Turn Coat, bludgeoning his mind with the memory of every horrible, nasty thing he's ever seen and experienced in order to desensitize himself and recover his stability after viewing The Naagloshi with his Sight.

In the Erebus Sequence, this is given to someone without their knowledge; Rafaela has been secretly building up Lucien's immunity to the poison Golia uses due to the (correct) fear that it will eventually be needed.

In the continuation to The Day of the Triffids, The night of the Triffids, this turns out to be the way in which humanity can finally take the world back from the triffids. This is taken from the original Day of the Triffids, in which the narrator is only alive because a career of working with Triffids has led to him building up enough resistance to survive the sting that put him in hospital.

One 1632 short story centered around a poisoning that was originally suspected to be murder until it was discovered to be an accidental suicide. The dead man had been dosing himself with arsenic regularly in an attempt to build up an immunity. Unfortunately, his regular supplier had been selling him adulterated drugs, so his immunity wasn't built up anywhere near as much as he thought. After buying a new supply from a different chemist, who sold him pure arsenic, he took what he thought was the appropriate dosage for his regimen, which was based on the weaker drugs of his first supplier. The massive dose of pure arsenic overpowered his limited immunity and killed him.

Live-Action TV

In an episode of Babylon 5, "Intersections in Real Time", Sheridan is being held prisoner by EarthGov and subjected to interrogation. At one point, the interrogator is eating a sandwich with delight and offers it to Sheridan, pointing out that he's eating it with no ill effects. And he assures Sheridan they have no desire to kill him until after he's been broken. It's only after Sheridan finishes eating that the interrogator mentions that it contained a powerful toxin that the latter has built an immunity to. The toxin doesn't kill Sheridan, but makes him very sick, as intended.

The Cape, a 2010-2011 series, used it when the titular character, learning he was dealing with a poisoner, took it upon himself to work up an immunity to everything the guy was likely to utilize. We didn't get to see if the immunities actually HELD, because the guy just tried to run him through.

The Twilight Zone (1959) episode "The Jeopardy Room". A Soviet commissar tricks a defector into drinking wine mixed with a sleep drug by drinking first. He built up an immunity to the drug by repeatedly taking increasing doses over time.

In The Vampire Diaries Katherine has built up an immunity to vervain, she can still get disabled by it if taken by surprise by a large enough dose but she gets over it much faster. Stefan uses this technique to get over his addiction to human blood.

In Stargate SG-1, a single shot from a Zat'nik'tel will typically cause extreme pain and/or unconsciousness in subjects. However it seems that years of exposure to hits from this kind of weapon is enough to build up a tolerance. In later seasons, we routinely see team-members who've been shot with a Zat suffer only mild discomfort and quickly shrug it off, while those who've never been Zatted before get consistently knocked out. This ends up being a plot point in an episode, where O'Neill has to run to the stargate in order to activate it and force the local Energy Beings away, allowing the rest of the team to flee. He uses zat shots to temporarily make his ionized body repel the creatures, but the effect wears off after a minute or so. He can't zat himself again, as a second zat shot within a certain time frame is fatal. Luckily, Teal'c shows up just in time and zats the ground next to O'Neill to the same effect. Wonder why no-one thought of that one before.

Wraith stunners from Stargate Atlantis seem to have the same effect as well: a glancing hit to a limb sometimes fails to knock out characters like Ronon who have been shot many times before.

In a sketch in Human Giant a contestant practices for a literal gas guzzling contest (as in drinking gallons of petrol and yes it shown to be as deadly as that sounds) by drinking various poisons including paint thinner to build up an an immunity. he wins but doesn't have a car.

In one episode of NCIS, the victim turns out to have been a hit man and his murderer is one of his intended victims. He used snake venom, and the woman kept snakes and developed immunity, although she didn't specify whether this was her intention or just a side-effect of her preferred pets.

In 1000 Ways to Die, a man decided to pick up a spider and let it bite him to gain immunity to its venom. Naturally, since he had no idea what he was doing, the bite kills him.

In the Halloween episode of Game Shakers, "Scared Tripless, this was part of the prank Double G played on the kids, primarily his son. Since the previous Halloween, he had been taking small amounts of venom so he can fake his death after being bitten by a snake. While it is successful, he forgets that snake bites can become infected and the doctors have to give him a shot in his butt to prevent it.

There was an episode of an old show (can't recall the name), where a child was bitten by a rare breed of a snake. It turned out that there was just enough anti-venom available for a single dose. Unfortunately, a doctor ends up accidentally also getting bitten by the same snake. She chooses to let the child have the anti-venom. Luckily, there's a hermit snake wrangler, who has developed an immunity to the same venom, and he eventually allows his blood to be drawn and distilled into an impromptu anti-venom for the doctor.

One clip on World's Dumbest... features mystics from India who spend their lives building up a tolerance for cobra venom. They then hold a competition to see who can take the most bites before conking out.

Tabletop Games

In Warhammer Fantasy, ogre butchers (wizards that eats all kinds of dangerous things to cast spells) have the immune to poison rule, so one would assume they have built up a very handy poison immunity.

Spirit of the Century features an endurance stunt called Developed Immunities that makes a character flat-out immune to "common" poisons and gives +2 or +6 to rolls to resist uncommon ones, depending on whether or not the character has encountered them before. A character who combines this stunt with a sufficiently high Endurance trait has nothing to fear from any save perhaps the most outlandish poisons. (As they run on their own versions of the same system, the exact same stunt can also be found in Starblazer Adventures and Legends Of Anglerre. The also related but somewhat less pulp-ish The Dresden Files omits it.)

1st Edition: The Rogues Gallery. The NPC Lassiviren the Dark has taken steadily increasing doses of poison over the years. As a result, few poisons affect him.

2nd Edition:

Drow of the Underdark. During their training, drow have successively larger doses of drow sleep poison and various spider venoms administered to them. This gives them poison resistance ranging from +4 vs. random ingested poisons to +7 vs. spiders' and their own sleep poison.

Dark Sun boxed set DSE1 Dragon's Crown, book "The Road of Fire". The poisoner Wheelock is immune to all poisons found on Athas because of years of exposure to them.

3rd Edition:

Members of the Assassin Prestige Class received increasing saving throw bonuses to poison as they went up in level due to their use of and exposure to poisons.

Supplement Creature Collection. The Ubantu tribesmen coat their weapons with poison. They've developed a racial immunity to it due to generations of exposure.

In Paizo's Tabletop Game//Pathfinder, the Alchemist class slowly gains resistance to poison over the first 9 levels of their career before finally becoming completely immune at level ten, presumably using this method.

Classic Traveller supplement SORAG: Handbook of Organization and Equipment. During the PC creation process a SORAG agent can be assigned to the Medical Division. During the assignment the agent can be given an immunity to Truth Drug by injections of small doses of the drug over an extended period under carefully controlled conditions to build up the body's natural resistance. There is a small chance of the agent's body resisting the treatment, in which case no immunity is gained and the agent's Endurance drops by 1 point.

Hollow Earth Expedition, supplement Mysteries of the Hollow Earth. Cannibal tribes are known for their skill in creating poisons. Some of them include small doses of poison in their meals to build up an immunity to them.

In Mice and Mystics, the first mouse to be captured with at least one poison wound will not receive poison wounds until the end of the chapter.

Video Games

NetHack (what else?) features varieties of poisonous meats that have a slight chance of providing permanent poison resistance when consumed. You can similarly gain resistance to heat, cold and electricity by eating certain corpses. You can even get immunity to Disintegrator Rays that way.

A similar Roguelike game, ADOM, gives poison resistance to players who eat corpses of giant spiders.

Subverted in Ragnarok (Roguelike). While it's possible to acquire poison immunity in a similar manner (though most venomous animals are still poisonous to eat), the poison of the phantom asp is so potent it has a chance to kill even through supposed "immunity."

One country has a sighting ceremony where the knight and the ruler mix drops of their blood in a bowl and sip from it. One character builds up a tolerance until he can make his blood lethal to others.

The only reason that Riou can eat his sister's "food" is because he's developed an immunity to it.

In Final Fantasy: Crystal Chronicles, you meet the Selkie De Nam, who decides that the best way to deal with the deadly Miasma is to try to build up a resistance to it by drinking water with miasma mixed in. It doesn't end well.

In Lost Souls MUD, once you have any degree of poison resistance, exposure to poison will develop it further.

One quest has a werewolf character who claims to have overcome his weakness to wolfsbane herb by posing as a merchant and selling it to werewolf hunters, while secretly exposing himself to small quantities of it.

One World of Warcraft Horde quest has the player fight venomhide ravasaurs (venomous raptors) and get splashed with their toxic blood in order to become immune. This is the first step to getting a venomhide ravasaur mount.

Worgen have a racial ability, Aberration, which reduces the duration of curses and diseases they are afflicted with. Presumably because they're already afflicted with the Worgen curse.

Fallout: New Vegas gives you increased resistance to broken limbs if you've already broken them 50 times. Somehow. It's best not to think about it when the cure for a broken limb is often "sleep it off". Even the game acknowledges this with the reward text "Repeatedly breaking bones has led them to become stronger (somehow)."

Actually truth in television. Because adult bones usually lose calcium slowly after time they tend to become stronger after the process is reversed during the knitting of bones.

In the Dead Money DLC, Dean Domino is resistant to the poisonous cloud of the Sierra Madre due to having been a resident of the place for 200 years. Having him as a companion will grant you a temporary immunity towards the cloud.

In Rune Factory 3, your protagonist has a "Poison" skill that goes up whenever he is poisoned by the enemy, or whenever he succesfully poisons one of them with an attack. One of the benefits of raising it is it makes you harder to be poisoned.

In Dragon Age: Origins Oghren has spent so many years mistreating alcohol, that he no longer suffers any negative effects from whatever he drinks. Taken further in Awakening where during the Joining ceremony, upon drinking the concoction (which contains darkspawn blood among other unpleasant ingredients), which typically renders the new Wardens unconscious, he merely burpsand claims it was "not bad".

In additon Awakening introduces the Vitality skill tree, which provides health bonuses. One of the descriptions mentions the character consuming small amounts of toxic materials to build up resistances.

In the Monster Hunter series, the titular monsters get an increase in poison resistance each time the poison status effect is applied. The same is true for KO, paralysis and traps.

In the final route of Duel Savior Destiny following the end of Mudou and Kaede's Duel Boss Fight the latter collapses after winning the fight due to to poison. She returns in the endgame citing this for why it wasn't an outright double kill.

In Mass Effect 2, failure to realise that without constant supervision, a sedated Shepard won't stay that way for long, ends up foiling the Indoctrinated Alliance agents in The Arrival. One medical report in The Arrival even mentions their frustration that it was necessary to increase every round of sedatives administered because Shepard's system simply grew immune to the previous dose, given only four hours earlier.

Probably justified by the same cybernetics that allow them to survive drinking ryncol.

Throughout the series, this is a racial trait of the Argonians. Living in the BlackMarsh with so many poisonous and toxic lifeforms has made the Argonians almost totally immune to natural and magical poisons. Likewise, the Bosmer (Wood Elves) and Redguards typically have lesser (around 50%) natural racial resistances to poisons.

In background lore, the Khajiit are far less susceptible to the Fantastic Drug, Moon Sugar. Moon Sugar is sacred in their culture, and they believe it to be "crystallized moonlight." Nearly all of their food uses it in some form or another, hardening their bodies to it. Still, overeating the sweetest of Khajiit foods can overwhelm even their resistance.

In Skyrim, an alchemy perk 'snakeblood' gives you 50% resistance to poison, which follows perks that involve creating poisons and eating ingredients — implying you've had so much passive exposure to the various poisons that they don't work on you any more.

Etrian Odyssey has a mechanic where inflicting a status ailment or bind on an enemy or ally will increase that character's resistance to that effect for the remainder of the battle. In the fourth game, Arcanists have a skill called "Release Spell" that undoes this.

In Batman: Arkham Knight, Scarecrow has acquired partial immunity to his own fear toxin. However, a large enough dose can overpower it, and like in the Blackest Night example, he still does fear Batman.

In The Legend of Zelda: Breath of the Wild, the Zora are portrayed as being especially vulnerable to electricity, which is inconvenient because Shock Arrows are needed to incapacitate the Divine Beast Vah Ruta that has been causing havoc for the Lanayru Province. King Dorephan and Prince Sidon decide to seek help from Hylians, who lack said vulnerability, but one Zora named Seggin instead unsuccessfully tries to develop an immunity to electricity by repeatedly touching a Shock Arrow.

Gilgamesh Wulfenbach has immunity to many many things. Because his father "figures that a ruler should be... hard to kill", what with the people across all of Europe who're upset at killing that Mad Scientist or the process of bombing this town... which extends to his heir. This came in useful in the arc where Tarvek suffered a particularly nasty and rare disease — Gil was able to disregard the risk of infection.

Those with Smoke Knight training are also immune to ordinary soporifics, as seen with Violetta and Martelus during the tea break at the Corbettites. Unfortunately for Martelus, those training sessions didn't include immunity to a sap to the head.

Keychain of Creation: Besides disturbing quantities of alcohol, Ten Winds has reportedly been exposed to toxins, drugs and pharmaceuticals of all kinds and quantities from across Creation over his multi-century lifespan. Stack that on top of his already supernatural Exalted metabolism and you have someone who is very hard to poison.

In Something*Positive, Kharisma tries to kill Avagadro with cyanide, which he has built up an immunity to after being poisoned by so many people over so many years. He says that he has grown accustomed to the taste, and now puts it on his cereal.

Spacetrawler: Dmitri believes that a person can become immune to stun guns, and has started shooting himself repeatedly in order to acquire it. Results: he acquires a taste for stun-gun shots. And immunity. In that order.

In Dino Attack RPG, Amanda Claw built up immunities to several different poisons and toxins by taking small doses during her years as Silencia Venomosa. This protected her from the poisonous gas in the Mindstorms, Inc. office building. She also hoped this would protect her from the XERRD toxins, but evidently that is one immunity she never acquired; still, she held out longer than most of her fellow Dino Attack agents.

Sylvester, in Twig, is the recipient of the Wyvern formula, which consists of a variety of natural toxins and poisons which is regularly injected into his brain in order to improve brain plasticity and healing, which grants him the ability to rapidly retrain himself in different skillsets. As a side effect, he's developed resistances to a variety of common poisons, though there's still more that can beat him.

In the Super Mario Logan episode, "Shrek's Diet", it is revealed that the diabetes Shrek got from eating nothing but cheesecake his entire life has caused his body to build up an immunity to diabetes.

A milder example, as it's not really a poison. In The Nostalgia Critic's music video "F**king Love Christmas", Critic sings a psychotic metal song about how much he loves the holiday. He terrifies Malcolm and Tamara so much that Malcolm has to tranquilize him. He then sings that he built up an immunity to tranquilizers because of his insane love of Christmas.

In the tgchan quest Fen Quest, it's mentioned that immunity to Tomato's deadly venom must be periodically "maintained" by ingesting some of it, otherwise it wears off over time. When his sister Cheese is accidentally stung after months apart, they determine she still has enough resistance to survive unaided, but will nonetheless get gravely ill without antidote.

Western Animation

In Frisky Dingo, Killface tries to poison Phil with a "vitoxin" poison, but finds out Phil built up an immunity to it, coincidentally using small doses to help him lose weight. Unfortunately for Phil he didn't build up an immunity to be accidentally shot in the head by a sniper aiming for someone else.

In Metalocalypse, Pickles is immune to the mind-erasing effects of Totally Awesome Sweet Alabama Liquid Snake, and every other drug as well, as the result of doing "government weed" daily since the age of 6.

Snake Eyes in G.I. Joe: Renegades takes multiple hits from poison darts thanks to a built up immunity. They're still enough to weaken him though.

In one segment of Peabody and Sherman, Mr. Peabody uses this trope to help the husband of Lucrezia Borgia.

In Young Justice, Aqualad reveals that he is "largely immune" to the jellyfish toxin that Cheshire uses to coat her darts. Largely doesn't mean completely, though: he was weakened by it, more with each dose. Of course this may be a result of his Atlantean biology, and not an acquired trait.

Dan from Dan Vs. has been hit with tear gas and pepper spray so many times that he doesn't feel their effects anymore. He can even tell the differences.

Nigel Thornberry claims in The Wild Thornberrys that he's developed an immunity to poisonous plants by rubbing their juices all over his body.

Dale Gribble in King of the Hill was unaffected by police tear gas stating that he kills squirrels with stronger gases. Given that he's an exterminator spraying poisonous gases without wearing a mask and while his health slowly deteriorates (alongside with smoking).

In the "Cartoon Smokers" sketch from the Robot Chicken episode, "Triple Hot Dog Sandwich on Wheat", Olive Oyl is among the famous cartoon characters being treated for lung cancer in a hospital, due to years of exposure to secondhand smoke from Popeye. Ironically, Popeye is just fine due to an immunity to lung cancer developed by the antioxidants in his spinach.

The titular Archer has been poisoned and drugged so many times in his line of work, he can metabolize and shake off toxins with ludicrous speed.

Real Life

As noted above, the official term for this (Mithridatism) comes from King Mithridates VI, a king of Pontus. He feared assassination so badly that he took small doses of poison regularly in order to become immune to the poison's effects. This backfired when the king was eventually conquered. He attempted to commit suicide by poisoning himself only to find that he was immune; depending on the version of the story you hear, he then either fell upon his sword or had an underling run him through. In either case, the poem says it best: "Mithridates, he died old."

Supposedly this was a very common practice amongst the upper classes in Ancient Rome. At any rate, it is referenced in the Cambridge Latin textbook series with a similar outcome to Mithridates.

Human body quickly builds up tolerance to most alkaloids (ranging from the relatively harmless caffeine to opiates, nicotine, atropine or cocaine), which drives people slowly to higher doses and addiction. Nicotine from tobacco, in pure form, can kill a fully grown human in amounts as small as 30 mg, which is 1/16th of a peppercorn, and during the 19th century had been used for assassinations, until forensic physicians discovered a way to detect it.

The movie Finding Nemo posits this as the reason clownfish can survive life among sea anemones — Marlin insists on Nemo brushing himself against the tendrils each morning in the vein of a human parent telling a child to brush their teeth thoroughly. Scientific theories vary on whether this is Truth in Television or not.

Haast: "It was risky, but I was cautious. When I started in 1948, a doctor said he wouldn't give me a nickel for me living two years. Well, I'm still here, but the doctor died of a coronary."

According to Deadliest Warrior, the African warlord Shaka Zulu spat poison into his opponent's eyes during battle. He avoided its effects himself by this method, eating small pieces of the plant it came from for years. This may or may not be true.

While you can't build up an immunity to arsenic, you can build up a tolerance. When American soldiers came to the UK in World War II those stationed in Cornwall often came down with arsenic poisoning from the water that the locals could drink with no problems.

This trope ended up backfiring when a man from Russia attempted to swallow small quantities of toxic mushrooms, arsenic, and cyanide daily to strengthen his body and protect himself from death. He later went into convulsions, slipped into a coma, and died without regaining consciousness. As seen here.

African Honey Badgers. Over their life time, they develop some immunity from the poisonous snakes, scorpions, and bees they regularly prey on. In fact, a male bitten on the cheek by a highly toxic puff adder showed signs of severe pain, but recovered fully within five hours. Watch it here.

According to some theories, the Aztecs got their red skin tone from the arsenic in their systems obtained by taking it over time to build up immunity.

In her autobiography, Venezuelan musician and metaphysican Conny Méndez claimed that, when she was young, one of her uncles decided to make the family immune to cyanide, and convinced them of sprinkling tiny quantities of the substance on their food and increasing the doses little by little. The thing ended some years later when an apothecary, alarmed with the huge quantities of cyanide bought by the family, sicced the police on them; by then the kids of the family were ingesting without ill effects enough cyanide to kill a normal adult.

A famous urban myth is Rasputin the Mad Monk - he supposedly had been taking minute doses of cyanide over a long period, and when his meal was poisoned, he ate it and walked away. Given that it should be impossible to build a resistance to cyanide, it's likely that it's not true; it's believed to be more likely that the poison had been counteracted by something else he ate during that meal.

The Rough-Skinned Newt has enough tetrodotoxin to kill a room full of adult humans, as a result of a ridiculous evolutionary arms race with Gardner snakes. The evidence suggests that each newt eaten adds more to the snake's overall resistance.

Allergy immunotherapy is a process that gradually reduces immune responses through exposure to minute doses of the allergen. After a few months the patient only needs a booster shot a couple times a year to maintain it.

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